Various pathologies of the heart decrease efficiency of the cardiac system. For example, reduced autonomic balance (an increase in sympathetic and a decrease in parasympathetic cardiac tone) has been shown to be associated with cardiac dysfunction, and in particular, left ventricular dysfunction. Additional pathologies which affect the manner and degree to which the heart chambers contract during a cardiac cycle also effect cardiac efficiency. For example, the heart pumps more effectively when the chambers contract in a coordinated manner, a result normally provided by specialized conduction pathways. Nominal function of these pathways synchronize contractions, promoting hemodynamic efficiency. Without synchronization, the heart's pumping efficiency is diminished.
During abnormal cardiac function, including during and after myocardial infarction, myocytes die and are replaced by scar tissue, which has different mechanical and elastic properties than functional myocardium. Over time, these tissues can become thin and expand, causing a redistribution of myocardial stresses over the heart, a phenomenon called remodeling. Eventually, this process leads to impaired mechanical function and heart failure.